Yup..."back then" you would arrange all your cards in a shoebox and then take a marker and make a diagonal mark from top left to bottom right JUST IN CASE you dropped said shoebox on the way to class to turn in your homework/take home test. Without that mark there's no easy way to recreate the correct order of the punch cards.
Source: dad was an engineering major in the early 70s.
This comment is extremely interesting to me as my first instinct would be numbering the cards w marker. But it makes far more sense to draw a line on the edge for visual sorting.
Source: dad was an engineering major in the early 70s.